Fig. 3.
Absorbance and emission spectra of aqueous solutions of NIR-emissive polymersomes. (A) Aqueous absorption and emission (Inset) spectra of emissive polymersomes containing NIRFs (i) PZn2,(ii) PZn3,(iii) PZn4, and (iv) PZn5. [Experimental conditions: λex = 510 nm. Note that these complexes possess subps S2-to-S1-state internal conversion times; hence, visible electronic excitation gives rise, with unit quantum efficiency, to the identical low-energy-emitting state that is accessed via NIR excitation (26).] Increasing conjugation length in PZn2–PZn5 augments the NIR absorption oscillator strength and shifts both the fluorophore absorption and corresponding emission maxima progressively to longer wavelengths (23–26). (B) Demonstration of facile fluorescence-wavelength modulation of vis- and NIR-emissive polymersomes. Emission bands of PZn2–PZn5 (A) are reproduced; other emission bands shown derive from polymersomes incorporating related ethynyl- and butadiynyl-bridged NIRFs (Table 2) (23, 24).